Heat-curable pulverulent coating agent consisting of a mixture of copolymers containing anhydrides and curing accelerators

ABSTRACT

The invention relates to heat-curable pulverulent coating agents, frequently also called powder lacquers, which are suitable for applying a coherent coating which possesses excellent properties after heat-curing.

United States Patent [1 1 Katsimbas I 1 I'IEAT-CURABLE PULVERULENTCOATING AGENT CONSISTING OF A MIXTURE OF COPOLYMERS CONTAININGANHYDRIDES AND CURING ACCELERATORS [75] Inventor: ThemistoklisKatsimbas, Homburg.

Germany [73] Assignee: Hoechst Aktiengesellschaft, Germany [22] Filed:May 30. 197-1 [21] Appl. No.: 474,414

[30] Foreign Application Priority Data June 26. 1973 Switzerland 9313/73[52] US. CL. 260/836; 117/132 BE; 260/837:

260/830 R; 260/830 TW; 260/835 [51] Int. Cl. C08L 63/00 1 1 Nov. 11,1975 Primary E.\umim'rPaul Lieberman Almrm'y. Agent. or FirmGordon W.Hueschen [57] ABSTRACT The invention relates to heat-curable pulverulentcoating agents. frequently also called powder lacquers. which aresuitable for applying a coherent coating which possesses excellentproperties after heat-curing.

11 Claims. No Drawings HEAT-C URABLE PULVERULENT COATING AGENTCONSISTING OF A MIXTURE OF COPOLYMERS CONTAINING ANHYDRIDES AND CURINGACCELERATORS BACKGROUND OF THE INVENTION It is already known tomanufacture heat-curable pulverulent coating agents based on copolymerswhich contain glycidyl groups, and to use such coating agents. However,such known products suffer from the disadvantage that they must bestoved at temperatures above 200C in order to obtain resistant films. Ifattempts are made to lower the stoving temperatures of such knownpulverulent coating agents by addition of accelerators, the effect isinadequate or the resulting films yellow already during the stovingprocess, and at times the adhesion is also interfered with.

Such known pulverulent coating agents are described in German publishedspecifications Nos. 2,240,312, 2,240,314, 2,240,315, 2,057,577,2,064,916, 2,214,650 and 2,122,313.

1. It is the task of the present invention to provide a heat-curablepulverulent coating agent which shows simultaneous improvements invarious directions compared to the known pulverulent coating agents. Oneobjective is that it should be possible to manufacture the. pulverulentcoating agents by simple mixing, homogenising fusion and conjointgrinding of the requisite components.

2. The pulverulent coating agent manufactured by thorough mixing,homogenising fusion and grinding should be storage-stable at thecustomary storage temperatures between about 40 and +40C.

3. The coating agent should after application, give very glossy,non-yellowing coatings of good levelling characteristics and freedomfrom blisters and craters, merely by stoving for about to 30 minutes atabout 150 to 180C.

4. The stoved films should not yellow and should not only exhibitexcellent weathering resistance but also substantially improvedresistance to organic solvents and chemicals, the comparison of theseproperties being with powder lacquers which are formulated on the basisof acrylate copolymers.

SUMMARY The subject of the invention is a pulverulent coating agent of amixture of A. a copolymer of relatively low molecular weight, whichcontains glycidyl groups and is a copolymer of several ethylenicallyunsaturated compounds,

B. at least on dicarboxylic acid anhydride in an amount corresonding to0.4 1.0 anhydride groups per epoxy group (glycidyl group) of thecopolymer and C. a curing accelerator in the form of an organic base,

D. a flow control agent in an amount of at least 0.05 per cent by weightof the mix t ure, which agent is a polymer of molecular weight (M of atleast 1,000 and has a glass transition temperature which is at least 50Clower than the glass transition temperature of the copolymer (A),characterised in that the component (A) consists of 84 to 94 per cent byweight of copolymers containing epoxide groups and hydroxyl groups,which copolymers have Durran softening points of about 90-120C and aresoluble in organic solvents and are produced from:

a. 6-24 per cent by weight of ethylenically unsaturated epoxide monomerswith 6-12 carbon atoms, of the general formula whereln R and R H- or CH;

b. 4-20 per cent by weight of hydroxyalkyl esters of acrylic acid ormethacrylic acid, with the hydroxylalkyl ester group being saturated andcontaining 2-4 C atoms,

c. 24-45 per cent by weight of acrylic acid esters or methacrylic acidesters of aliphatic saturated monoalcohols with l-8 carbon atoms and d.-55 per cent by weight of styrene or vinyltoluene, the component (B)consisting of 6-16 per cent by weight of at least one dicarboxylic acidanhydride with melting points of about 60l40C,

the component (C) consisting of 0.5 -l.8 per cent by weight ofN,N'-bis-(dimethylamino isobutylidene)- melamine and the optionalcomponent (D) consisting of a flow control agent and other customaryadditives.

In a preferred embodiment of the invention component (A) comprises:

a. 12 to 16 per cent by weight of glycidiyl methacrylate,

b. 14 to 18 per cent by weight of hydroxyethyl methacrylate,

c. to 38 per cent by weight of ethyl acrylate and d. to 42 per cent byweight of styrene.

A special embodiment of the invention relates to a pulverulent coatingagent according to patent claim 1, characterised in that component (A)consists of a copolymer produced from:

a. 12 to 16 per cent by weight of glycidly methacrylate,

b. 12 to 16 per cent by weight of hydroxyethyl methacrylate,

c. 18 to 22 per cent by weight of n-butyl acrylate and 7 to 1 l per centby weight of methyl methacrylate,

d. 38 to 42 per cent by weight of styrene.

A further embodiment of the invention relates to a pulverulent coatingagent according to patent claim 1. characterised in that a component (A)consists of a copolymer made of:

a. 12 to 16 per cent by weight of glycidyl methacrylate,

b. 12 to 16 per cent by weight of hydroxyethyl methacrylate,

c. 18 to 22 per cent by weight of n-butyl acrylate and 14 to 20 per centby weight of methyl methacry- 3 late,

(1. 28 to 32 per cent by weight of styrene.

A further special embodiment of the invention relates to a pulverulentcoating agent according to patent claim 1, characterised in that thecomponent (A) consists of a copolymer made of:

a. 12 to 16 per cent by weight of glycidyl methacrylate,

b. 12 to 16 per cent by weight of hydroxyethyl methacrylate,

c. 32 to 36 per cent by weight of n-butyl methacrylate and d) 28 to 36per cent by weight of styrene.

A further embodiment of the present invention relates to the use of thepulverulent coating agent according to one of the claims 1 to as powderlacquer which is storage stable between 40C and +40C and which giveshighly glossy, non-yellowing coatings after stoving at about 150C to180C for about to 30 minutes, which show good levelling and which arefree from blisters and craters.

As component (a) it is possible to use ethylenically unsaturated epoxymonomers with 6-12 carbon atoms, of the general formula These include:glycidyl acrylate, glydicyl methacrylate, allyl glycidyl ether,methallyl, glycidyl ether, glycidyl crotonate, vinyl glycidyl ether,allyl glycidyl maleate, allyl glycidyl phthalate and butadient monoxide.

As component (b) it is possible to use hydroxyalkyl esters of acrylicacid or methacrylic acid, such as hydroxyethyl acrylate, hydroxyethylmetacrylate, hydroxypropyl acrylate and hydroxybutyl acrylate.

As component (c) it is possible to use acrylic acid esters ormethacrylic acid esters of aliphatic saturated monoalcohols with 1-8carbon atoms, namely: methyl methacrylate, ethyl acrylate, butylacrylate, 2-ethy1- hexyl acrylate, Z-ethylhexyl methacrylate, isobutylacrylate and butyl methacrylate. Ethyl acrylate or butyl methacrylateare use preferentially.

Styrene or vinyltoluene are co-used as component ((1).

The copolymers are manufactured according to known processes of bulkpolymerisation, solution polymerisation or dispersion polymerisation,preferably by solution polymerisation. Such processes are described, forexamples, in the book Methoden der Organischen Chemie" (Methods ofOrganic Chemistry),

4 Houben-Weyl, 4th edition, volume 14/1, pages 24 to 556 1961 r if thepolymerisation is carried out in solution, solvents such as methylenechloride, ethanol, isopropanol, n-propanol, n-butanol, iso-butanol,tert.- butanol, acetic acid methyl ester to butyl ester, acetone, methylethyl ketone, benzene. toluene und others can be employed.

The polymerisation is carried out at temperatures of 40 to about C.

As initiators it is possible to employ, for example, percarbonates,per-esters, such as tert.-butyl perpivalate, or peroctoate, benzoylperoxide, o-methoxybenzoyl peroxide, dichlorobenzoyl peroxide orazodiisobutyrodinitrile, in amounts of 0.5 to 8% by weight based onmonomers.

Further, customary molecular weight regulators, such asn-dodecylmercaptan or tert.-dodecylmercaptan, can be co-used.

The copolymer solution is freed from the solvent by distilling thelatter off in vacuo, or in suitable apparatus, preferably evaporatorscrews, at temperatures of about 90 to 160C, and the residue is cooled,granulated and ground. However, the product can also be isolated inaccordance with other processes, say by spray drying, removal of thesolvent with steam and simultaneously disperging in water, orprecipitation by means of water from a water-miscible solvent.

As dicarboxylic acid anhydrides (component B) it is possible to usephthalic anhydride, p-chlorophthalic anhydride, tetrabromophthalicanhydride, cyclohexane-l,2-dicarboxylic acid anhydride, 4-methylhexane-1,2dicarboxylic acid anhydride, cyclopentane,1,2- dicarboxylic acidanhydride, dodecylsuccinie anhydride, succinic anhydride, maleicanhydride, methylsuccinic anhydride and polyazelaic anhydride. ingeneral, anhydrides having a melting point in the range of 60 to C arepreferred.

N',N'-bis-(dimethylamino isobutylidene)-melamine is used as component(C). The manufacture of this compound is described in German publishedspecification No. 1,620,178, on page 5, in Example 1. Further, thiscompound has been described by the same applicant, in German publishedspecification No. 1,645,190,

as a curing agent for epoxide resins. According to this priordescription, this curing agent is used together with epoxide compounds,in amounts of 2 to 25 per cent by weight, preferably 2 to 10 per cent byweight, relative to the amount of the epoxide compound, for the purposesof a curing agent. However, it was not known, and also not to beexpected, that this known curing agent would, when used in amounts ofless than 2 percent of weight, together with dicarboxylic acidanhydrides, exert an accelerating action on the anhydride curing of theepoxide resins.

As the flow control agent (D) it is possible to use, in the pulverulentcoating agent, an acylic polymer having a glass transition temperaturewhich is at least 50C lower than the glass transition temperature of thecopolymer used in the mixture. Preferred acrylic polymers which can beused as flow control agents are polylauryl acrylate, poly-butyl ac'ylate, poly-(Z-ethylhexyl acrylate), polylauryl methacrylate andpolyisodecyl methacrylate.

The flow control agent can also be a fluorinated polymer which at thestoving temperature of the powder mixture has a lower surface tensionthan has the copolymer used in the mixture. If a fluorinated polymer isused as the flow control agent, esters of polyethylene glycol orpolypropylene glycol and fluorinated fatty acids are preferred. Anexample of a suitable flow control agent is an ester of polyethyleneglycol, of molecular weight greater than 2,500, but below 20,000, andperfluorooetanoic acid. Furthermore, levelling agents, such assilicones, polyesters, ketone resins, epoxide resins and cellulosederivatives can be added to the melts. It is also possible to addpigments, levelling agents and other additives customary in such coatingagents.

The solvent-free, optionally pigmented components, which are brittle inthe non-crosslinked state, are ground to particles of about 100 to 300p, fused at about 951 C with good mixing or kneading, cooled, againground, after solidification, to a particle size of 30 to 120 u, andoptionally screened according to particle size.

The pulverulent coating agents to be used according to the invention arestill free-flowing at temperatures of at least 30-40C, preferably 40C,have flow temperatures of approx. 80 to 120C and are stoved attemperatures above 130C, preferably at 160 to 180C, whereuponcrosslinking occurs.

The pulverulent coating agents are applied to suitable substrates,especially metals, in accordance with known methods, for example theelectrostatic powder spraying process.

The stoved films of the pulverulent coating agents used according to theinvention have excellent adhesion and hardness coupled with elasticity.Furthermore, they are distinguished by high gloss, very good weatheringresistance and very good resistance to wash liquors.

The powders are used for coating household utensils, metal parts used incar manufacture, metal parts which are exposed to weathering factors,such as facade panels, pipes, wire braids, equipment used in forestryand agriculture and other metal articles for interior architecture.

The examples which follow describe the manufacture of the powders andtheir use as electrostatically sprayable powders. The parts andpercentages quoted in the examples are by weight, unless statedotherwise.

EXAMPLE 1 424 g of toluene are introduced into a two-liter stirring potequipped with a reflux condenser, thermometer and two dropping funnels.The toluene is brought to the reflux temperature by heating to about 112C and two monomeric mixtures, namely (a) 429 g of styrene, 509 g ofethyl acrylate, 214 g of hydroxyethyl methacrylate and 188 g of glycidylmethacrylate and (b) 62 g of tert.-butyl peroctoate and g of toluene aresimultaneously added dropwise thereto over the course of 4 hours. Themixture is then kept under reflux for a further hour and during thistime an additional 4 g of tert.-butyl peroctoate are added dropwise. Themixture is then afterpolymerised for further 2 hours under reflux atabout 1 18l 20C. The resulting copolymer has a Gardner-Holdt viscosityof 0-1. measured as a 50% strength solution in toluene at 20C. Afteraddition of 5.5 g of a flow control agent (Modaflow of Messrs. MonsantoChemicals), the toluene is distilled off at up to 160C and under reducedpressure at 40 mm Hg, giving a brittle clear solid resin which canreadily be powdered.

300 g of the resulting solid resin are ground together with 32 g of amixture of dicarboxylic acid anhydride and curing accelerators,consisting of 92% by weight of tetrahydrophthalic anhydride and 8% byweight of N,- N'-bis-(dimethylamino isobutylidene)-melamine. and anadded pigment, namely 132 g of titanium dioxide (of the rutile type) ofparticle size about -200 u. The powder mixture is then mixed for 4minutes in an extruder at C, the melt is shockchilled to roomtemperature and the product is ground to give particles of approx. 80 u.

The pulverulent coating is applied by means of an electro-spray gun ontodegreased phosphatised galvanised steel sheets and then stoved. for 30minutes at C.

Coatings having the following properties are obtained (wherein 0 meansvery good and 5 means bad") 2 Coating thickness. p: 44-48 Le\e|ling.assessed visually: 0-1 Folding test; 0 Yellowing: 0-1 Xylene resistance.2 hours: (1 Pencil hardness: H5 Erichsen deep-drawing value: 9.4 mmGloss by Lange's method: 103 Grid-cut test: 0

EXAMPLE 2 The procedure followed is as in Example 1, but as amodification a copolymer is produced from the following monomer mixture:483 g of styrene, 455 g of ethyl acrylate, 214 g of hydroxyethylmctacrylate and 188 g of glycidyl methacrylate. The copolymer obtainedis converted to a pulverulent coating agent in accordance with theinstructions in Example 1.

EXAMPLE 3 The procedure followed is as in Example 1, but as amodification, a copolymer is produced from the following monomermixture: 402 g of styrene, 480 g of ethyl acrylate, 188 g ofhydroxyethyl methacrylate. 122 g of methyl methacrylate and 148 g ofglycidyl methycrylate. 300 g of the solid resin obtained are ground with20 g of a dicarboxylic acid anhydride and curing accelerator mixtureaccording to Example I.

The stoved coatings show similar properties, with better flow, than thecoatings which have been produced according to Example 1.

EXAMPLE 4 The procedure followed is as in Example 1, but as amodification, a copolymer is produced from the following monomermixture: 402 g of styrene, 480 g of butyl methacrylate, 188 g ofhydroxyl methacrylate, 122 g of methylmethacrylate and 148 g of glycidylmethacrylate. Instead of peroctoate, 46 g of benzoyl peroxide are used.The copolymer is then converted to a pulverulent coating agent in themanner indicated in Example 1.

EXAMPLE 5 490 g of toluene are introduced into a two-liter stirring potequipped with a reflux condenser, thermometer and two dropping funnels.The toluene is brought to reflux temperature by heating to about I 12Cand two monomeric mixtures, namely 7 (a) 500 g of styrene, 250 g ofbutyl acrylate, 200 g of hydroxyethyl methacrylate, 200 g of glycidylmetacrylate and 100 g of methyl metacrylate and (b) 44 g of toluene and64 g of tert.-butylperoctoate are simultaneously added dropwise theretoover the course of 4 hours.

The mixture is then kept under reflux for further 2 hours and duringthis time an additional 2 g of tertbutyl peroctoate are added dropwise.The mixture is then afterpolymerised for further 2 hours under reflux atabout 1 l2l 14C. The resulting copolymer has a Gardner-Holdt viscosityof M-N measured as a 50% strength solution in toluene at C. Afteraddition of 2.4 g of a flow control agent (Modaflow of Messrs. MonsantoChemicals). the toluene is distilled off by heating to I60C and underreduced pressure at 40 mm Hg. giving a brittle clear solid resin whichcan readily be powdered.

EXAMPLE 6 The procedure followed is as in Example 5. but as amodification a copolymer is produced from the following monomer mixture:

(a) 375 g of styrene. 225 g of methyl methacrylate.

200 g of hydroxyethyl methacrylate. 200 g of glycidyl methaerylate and250 g of butyl acrylate and (b) is the same as in Example 5.

The obtained copolymer is converted to a pulverulent coating agent inaccordance with the instructions in Example 5. The coatings show goodproperties.

EXAMPLE 7 The procedure followed is as in Example I. but as amodification a copolymer is produced from the following monomer mixture:

(21) 425 g of styrene, 425 g of butylacrylate, 200 g of hydroxyethylmethacrylate and 200 g of glycidyl methacrylate and (b) is the same asin Example 5.

The copolymer obtained is converted to a pulverulent coating agent inaccordance with the instructions in Example l, which coatings show goodproperties.

The coating agents produced from copolymers made according to Examples 5to 7 give coatings of very good elasticity, Erichsen deep-drawing valuesover 6 mm and good resistance against xylene after having been appliedas powder and after stoving at 160C for minutes.

What is claimed is:

l. Pulverulent coating agent of a mixture of A. a copolymer ofrelatively low molecular weight, which contains glycidyl groups and is acopolymer of several ethylenically unsaturated compounds,

B. at least one dicarboxylic acid anhydride in an amount correspondingto 0.4 l .0 anhydride groups per epoxy group (glycidyl group) of thecopolymer and C. a curing accelerator in the form of an organic base.

D. a flow control agent in an amount of at least 0.05 per cent by weightof the mixture, which agent is a polymer of molecular weight. n) of atleast L000 and has a glass transition temperature which is at least 50Clower than the glass transition temperature of the copolymer (A),characterised in that the component (A) consists of 84 to 94 per 8 centby weight of copolymers containing epoxide groups and hydroxyl groups.which copolymers have Durran softening points of about l20C and aresoluble in organic solvents and which consist essentially of: a. 6-24per cent by weight of ethylenically unsaturated epoxide monomers with6-12 carbon atoms. of the general formula b. 4-20 per cent by weight ofhydroxyalkyl esters of acrylic acid or methacrylic acid. with thehydroxyalkyl ester group being saturated and containing 2-4 C atoms,

c. 24-45 per cent by weight of acrylic acid esters or methacrylic acidesters of aliphatic saturated monoalcohols with 1-8 carbon atoms and d.20-55 per cent by weight of styrene or vinyltoluene. the component (B)consisting of 6-]6 per cent by weight of at least one diearboxylic acidanhydride with melting points of about 60-l40C,

the component (C) consisting of 0.5 -l.8 per cent by weight ofN',N'-bis-(dimethylamino isobutylidene)-melamine and the optionalcomponent (D) consisting of a flow control agent and other customaryadditives.

2. Pulverulent coating agent according to claim 1, characterised in thatthe component (A) consists of a copolymer produced from a. 12 to H3 percent by weight of glycidyl methacrylate,

b. l4 to 18 per cent by weight of hydroxyethyl methacrylate,

c. 25 to 38 per cent by weight of ethyl acrylate and d. 30 to 42 percent by weight of styrene.

3. Pulverulent coating agent according to claim I, characterised in thatthe component (A) consists of a copolymer produced from:

a. l2 to 16 per cent by weight of glycidyl methacrylate,

b. l2 to l6 per cent by weight of hydroxyethyl methacrylate,

c. lie) to 22 per cent by weight of n-butyl acrylate and 7 to l l percent by weight of methyl methacrylate,

d. 38 to 42 per cent by weight of styrene.

4. Pulverulent coating agent according to patent claim 1, characterisedin that the component (A) consists of a copolymer made of a. 12 to 16per cent of glycidyl methacrylate,

b. 12 to 16 per cent by weight of hydroxyethyl methacrylate,

c. 32 to 36 per cent by weight of n-butyl methacrylate and d. 28 to 36per cent by weight of styrene.

5. Pulverulent coating agent according to claim 1, characterised in thatthe component (A) consists of a copolymer produced from:

a. 12 to 16 per cent by weight of glycidyl methacrylate,

b. 12 to 16 per cent by weight of hydroxyethyl methacrylate,

c. 34 to 38 per cent by weight of ethyl acrylate and 7 to 11 per cent byweight of methyl methacrylate,

d. 28 to 32 per cent by weight of styrene.

6. Pulverulent coating agent according to claim 1, characterised in thatthe component (A) consists of a copolymer produced from:

a. l2 to 16 per cent by weight of glycidyl methacrylate,

b. 12 to 16 per cent by weight of hydroxyethyl methacrylate,

c. 32 to 40 per cent by weight of n-butyl methacrylate and 7 to l l percent by weight of methyl methacrylate.

d. 28 to 32 per cent by weight of styrene.

7. A pulverulant coating agent according to claim 1 wherein thecopolymer component (A) contains as ethylenically unsaturated epoxidemonomer (a) a compound selected from the group consisting of glycidylacrylate, glycidyl methacrylate, allyl glycidyl ether, methallylglycidyl ether, glycidyl crotonate, vinyl glyci- 10 dyl ether, allylglycidyl maleate, ally] glycidyl phthalate and butadiene monoxide.

8. A pulverulent coating agent mixture according to claim 1 wherein thecopolymer component (A) contains as hydroxyalkyl ester component (b) acompound selected from the group consisting of hydroxyethyl acrylate,hydroxyethyl metacrylate, hydroxypropyl acrylate and hydroxybutylacrylate.

9. A pulverulent coating agent according to claim 1 wherein thecopolymer component (A) contains as component (c) a C, to C-aliphatically saturated monoalcohol ester of acrylic or methacrylicacid selected from the group consisting of methacrylate, ethylacrylate.butylacrylate. 2-ethylhexyl acrylate, Z-ethylhexyl methacrylate,isobutyl acrylate, and butyl methacrylate.

10. A method for coating a substrate which comprises applying to thesubstrate a film of the pulverulent coating agent of claim 1 by theelectrostatic powder spray process, and then stoving the filmedsubstrate at to C for about 15 to 30 minutes.

11. Pulverulent coating agent according to claim 1, characterised inthat the component (A) consists of a copolymer made of:

a. 12 to 16 per cent by weight to glycidyl mcthacrylate,

b. 12 to 16 per cent by weight of hydroxyethyl methacrylate.

c. 18 to 22 per cent by weight of n-butyl acrylate and 14 to 20 per centby weight of methyl methacrylate,

(1. 28 to 32 per cent by weight of styrene.

1. PULVERULENT COATING AGENT OF A MIXTURE OF A. A COPOLYMER OF RELATIVELY LOW MOLECULAR WEIGHT, WHICH CONTAINS GLYCIDYL GROUPS AND IS A COPOLYMER OF SEVERAL ETHYLENICALLY UNSATURATED COMPOUNDS, B. AT LEAST ONE DICARBOXYLIC ACID ANHYDRIDE IN AN AMOUNT CORRESPONDING TO 0.4 - 1.0 ANHYDRIDE GROUPS PER EPOXY GROUP (GLYCIDYL GROUP) OF THE COPOLYMER AND C. A CURING ACCELERATOR IN THE FORM OF AN ORGANIC BASE, D. A FLOW CONTROL AGENT IN AN AMOUNT OF AT LEAST 0.05 PER CENT BY WEIGHT OF THE MIXTURES, WHICH AGENT IS A POLYMER OF MOLECULAR WEIGHT, (MN) OF AT LEAST 1,000 AND HAS A GLASS TRANSITION TEMPERATURE WHICH IS AT LEAST 50*C LOWER THAN THE GLASS TRANSITION TEMPERATURE OF THE COPOLYMER (A), CHARACTERISED IN THAT THE COMPONENT (A) CONSISTS OF 84 TO 94 PER CENT BY WEIGHT OF COPOLYMERS CONTAINING EPOXIDE GROUPS AND HYDROXYL GROUPS, WHICH COPOLYMERS HAVE DURRAN SOFTENING POINTS OF ABOUT 90*-120*C AND ARE SOLUBLE IN ORGANIC SOLVENTS AND WHICH CONSIST ESSENTIALLY OF: A. 6-24 PER CENT BY WEIGHT OF ETHYLENICALLY UNSATURATED A EPOXIDE MONOMERS WITH 6-12 CARBON ATOMS, OF THE GENERAL FORMULA
 2. Pulverulent coating agent according to claim 1, characterised in that the component (A) consists of a copolymer produced from a. 12 to 16 per cent by weight of glycidyl methacrylate, b. 14 to 18 per cent by weight of hydroxyethyl methacrylate, c. 25 to 38 per cent by weight of ethyl acrylate and d. 30 to 42 per cent by weight of styrene.
 3. Pulverulent coating agent according to claim 1, characterised in that the component (A) consists of a copolymer produced from: a. 12 to 16 per cent by weight of glycidyl methacrylate, b. 12 to 16 per cent by weight of hydroxyethyl methacrylate, c. 18 to 22 per cent by weight of n-butyl acrylate and 7 to 11 per cent by weight of methyl methacrylate, d. 38 to 42 per cent by weight of styrene.
 4. Pulverulent coating agent according to patent claim 1, characterised in that the component (A) consists of a copolymer made of a. 12 to 16 per cent of glycidyl methacrylate, b. 12 to 16 per cent by weight of hydroxyethyl methacrylate, c. 32 to 36 per cent by weight of n-butyl methacrylate and d. 28 to 36 per cent by weight of styrene.
 5. Pulverulent coating agent according to claim 1, characterised in that the component (A) consists of a copolymer produced from: a. 12 to 16 per cent by weight of glycidyl methacrylate, b. 12 to 16 per cent by weight of hydroxyethyl methacrylate, c. 34 to 38 per cent by weight of ethyl acrylate and 7 to 11 per cent by weight of methyl methacrylate, d. 28 to 32 per cent by weight of styrene.
 6. Pulverulent coating agent according to claim 1, characterised in that the component (A) consists of a copolymer produced from: a. 12 to 16 per cent by weight of glycidyl methacrylate, b. 12 to 16 per cent by weight of hydroxyethyl methacrylate, c. 32 to 40 per cent by weight of n-butyl methacrylate and 7 to 11 per cent by weight of methyl methacrylate, d. 28 to 32 per cent by weight of styrene.
 7. A pulverulant coating agent according to claim 1 wherein the copolymer component (A) contains as ethylenically unsaturated epoxide monomer (a) a compound selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methallyl glycidyl ether, glycidyl crotonate, vinyl glycidyl ether, allyl glycidyl maleate, allyl glycidyl phthalate and butadiene monoxide.
 8. A pulverulent coating agent mixture according to claim 1 wherein the copolymer component (A) contains as hydroxyalkyl ester component (b) a compound selected from the group consisting of hydroxyethyl acrylate, hydroxyethyl metacrylate, hydroxypropyl acrylate and hydroxybutyl acrylate.
 9. A pulverulent coating agent according to claim 1 wherein the copolymer component (A) contains as component (c) a C1 to C8 -aliphatically saturated monoalcohol ester of acrylic or methacrylic acid selected from the group consisting of methacrylate, ethylacrylate, butylacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isobutyl acrylate, and butyl methacrylate.
 10. A method for coating a substrate which comprises applying to the substrate a film of the pulverulent coating agent of claim 1 by the electrostatic powder spray process, and then stoving the filmed substrate at 150* to 180*C for about 15 to 30 minutes.
 11. Pulverulent coating agent according to claim 1, characterised in that the component (A) consists of a copolymer made of: a. 12 to 16 per cent by weight to glycidyl methacrylate, b. 12 to 16 per cent by weight of hydroxyethyl methacrylate, c. 18 to 22 per cent by weight of n-butyl acrylate and 14 to 20 per cent by weight of methyl methacrylate, d. 28 to 32 per cent by weight of styrene. 